This invention relates generally to apparatus for the plasma enhanced thermal treatment of a material, and more specifically to apparatus for the plasma assisted thermal nitridation of silicon-bearing materials in which the plasma generation and thermal heating are independently controlled.
In certain applications in which an object such as a semiconductor device is subjected to a high temperature thermal treatment it has been found that the high temperature reaction is advantageously enhanced by simultaneous treatment with an rf plasma. For example, in the nitridation of a silicon surface by subjecting the surface to nitrogen bearing reactants at an elevated temperature, the nitridation process is improved by subjecting the reactants to an rf plasma in addition to the high temperature. By combining the rf plasma with the thermal treatment, the necessary temperature for the reaction can be reduced and the quality of the resulting silicon nitride film can be improved.
There have been a number of attempts to enhance high temperature thermal processing by the addition of plasma energy. For example, as is illustrated in U.S. Pat. No. 4,448,633, a plasma is generated outside a heated furnace and then that plasma is carried into the heated reaction zone. By the application of rf energy to plasma electrodes in the form of either an induction coil or capacitive means, an rf plasma is generated. Gaseous reactants in the presence of this plasma are raised to excited states and the reactant plasma species then flow into the heated reaction chamber where they react with a heated substrate. The reaction is the result of the combination of the high temperature environment and the excited plasma species. Although such a reaction can be efficiently utilized for growing films, or the like, on a small number of substrates, the process does not extend to the uniform formation of films on a large number of substrates. The plasma generated species have a finite lifetime; the further the plasma must travel from the location at which it is generated to the location at which it reacts with a heated substrate, the more dilute the concentration of plasma species. If a large number of substrates are to be processed, the plasma reactants may have to flow a considerable distance from the point at which they are generated. Those substrates closest to the plasma generation thus see a higher concentration of plasma species than do substrates located more distant from the plasma generation site. The non-uniformity of the plasma concentration across a number of substrates causes non-uniformity from one substrate to the next.
In order to overcome the plasma depletion effects, a number of attempts have been made to generate the plasma at the site of the heated reaction zone. For example, in U.S. Pat. No. 4,151,058, a hydrogen plasma is generated by an rf coil surrounding a reaction tube and the substrates to be acted upon. Heat for the reaction is provided by an adjacent radiant heat source. In other attempts to generate an in situ plasma, for example as illustrated in U.S. Pat. Nos. 4,298,629 and 4,486,461, a plasma is generated by an rf coil surrounding the reaction chamber. This same rf coil is also the source of heat for the reaction. In U.S. Pat. No. 4,298,629, the high temperature is achieved by induction heating a susceptor upon which the substrate rests. In U.S. Pat. No. 4,486,461 the high temperature is generated by induction heating a heater coil wrapped around the reaction zone. In each case the induction heating is accomplished by the same rf source which generates the plasma. In each of these attempts to overcome the plasma depletion effects, control of the reaction parameters is severely limited. Using a single energy source, for example, prevents the independent adjustment of plasma energy and temperature. Use of a radiant heat source provides less than the desired control of temperature.
In view of the foregoing, a need existed for processing apparatus which would provide the necessary control of processing parameters and overcome the deficiencies of the existing equipment.
It is therefore an object of this invention to provide an improved apparatus for the plasma enhanced thermal processing of silicon-bearing substrates.
It is another object of this invention to provide improved plasma enhanced thermal processing equipment having independent control of temperature and plasma parameters.
It is a further object of this invention to provide improved apparatus for the plasma enhanced treatment of semiconductor device substrates.
It is a still further object of this invention to provide improved apparatus for plasma enhanced thermal processing having means for protecting plasma electrodes from degredation at the reaction temperature.
It is yet another object of this invention to provide improved apparatus for the plasma enhanced thermal nitridation of semiconductor substrates.
It is another object of this invention to provide an improved process for the plasma enhanced in situ etching and subsequent thermally processing of a substrate.